Large scale synthesis of stable tricolor Zn(1-x)Cd(x)Se core/multishell nanocrystals via a facile phosphine-free colloidal method

Here we report a new "green" method to synthesize Zn(1-x)Cd(x)Se (x = 0-1) and stable red-green-blue tricolor Zn(1-x)Cd(x)Se core/shell nanocrystals using only low cost, phosphine-free and environmentally friendly reagents. The first excitonic absorption peak and photoluminescence (PL) position of the Zn(1-x)Cd(x)Se nanocrystals (the value of x is in the range 0.005-0.2) can be fixed to any position in the range 456-540 nm. There is no red or blue shift in the entire reaction process. Three similar sizes of alloyed Zn(1-x)Cd(x)Se nanocrystals with blue, green, and yellow emissions were successfully selected as cores to synthesize high quality blue, green, and red core/shell nanocrystal emitters. For the synthesis of core/shell nanocrystals with a high quantum yield (QY) and stability, the selection of shell materials has been proven to be very important. Therefore, alternative protocols have been used to optimize thick shell growth. ZnSe/ZnSe(x)S(1-x) and CdS/Zn(1-x)Cd(x)S have been found as an excellent middle multishell to overcoat between the alloyed Zn(1-x)Cd(x)Se core and ZnS outshell. The QYs of the as-synthesized core/shell alloyed Zn(1-x)Cd(x)Se nanocrystals can reach 40-75%. The Cd content is reduced to less than 0.1% for Zn(1 -x)Cd(x)Se core/shell nanocrystals with emissions in the range 456-540 nm. More than 15 g of high quality Zn(1-x)Cd(x)Se core/shell nanocrystals were prepared successfully in a large scale, one-pot reaction. Importantly, the emissions of such thick multishell nanocrystals are not susceptible to ligand loss and stability in various physiological conditions.     

Multistage Microfluidic Platform for the Continuous Synthesis of III–V Core/Shell Quantum Dots

We present a fully continuous chip microreactor‐based multistage platform for the synthesis of quantum dots with heterostructures. The use of custom‐designed chip reactors enables precise control of heating profiles and flow distribution across the microfluidic channels while conducting multistep reactions. The platform can be easily reconfigured by reconnecting the differently designed chip reactors allowing for screening of various reaction parameters during the synthesis of nanocrystals. III–V core/shell quantum dots are chosen as model reaction systems, including InP/ZnS, InP/ZnSe, InP/CdS and InAs/InP, which are prepared in flow using a maximum of six chip reactors in series.     

Synthesis CdSe(x)S(1-x) core/shell type quantum dots via one injection method

The photoluminescence quantum yield (PL-QY) of ternary colloidal CdSe(x)S(1-x) quantum dots (QDs), which were prepared by a one-injection method, enhances with increasing S content. The possible enhancement mechanism was explored by structural analysis via X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Both found that the enhancement of PL-QY of ternary CdSe(x)S(1-x) QDs strongly correlated with self-formed core/shell conformation in the non-coordination solution.     

Alloyed (ZnSe)(x)(CuInSe2)(1-x) and CuInSe(x)S(2-x) nanocrystals with a monophase zinc blende structure over the entire composition range

Metastable zinc blende CuInSe(2) nanocrystals were synthesized by a hot-injection approach. It was found that the lattice mismatches between zinc blende CuInSe(2) and ZnSe as well as CuInSe(2) and CuInS(2) are only 2.0% and 4.6%, respectively. Thus, alloyed (ZnSe)(x)(CuInSe(2))(1-x) and CuInSe(x)S(2-x) nanocrystals with a zinc blende structure have been successfully synthesized over the entire composition range, and the band gaps of alloys can be tuned in the range from 2.82 to 0.96 eV and 1.43 to 0.98 eV, respectively. These alloyed (ZnSe)(x)(CuInSe(2))(1-x) and CuInSe(x)S(2-x) nanocrystals with a broad tunable band gap have a high potential for photovoltaic and photocatalytic applications.     

Synthesis of InAs/CdSe/ZnSe core/shell1/shell2 structures with bright and stable near-infrared fluorescence

A complex InAs/CdSe/ZnSe core/shell1/shell2 (CSS) structure is synthesized, where the intermediate CdSe buffer layer decreases strain between the InAs core and the ZnSe outer shell. This structure leads to significantly improved fluorescence quantum yield as compared to previously prepared core/shell structures and enables growth of much thicker shells. The shell growth is done using a layer-by-layer method in which the shell cation and anion precursors are added sequentially allowing for excellent control, and a good size distribution is maintained throughout the entire growth process. The CSS structure is characterized using transmission electron microscopy, as well as by X-ray diffraction and X-ray photoelectron spectroscopy which provide evidence for shell growth. The quantum yield for CSS with small InAs cores reaches over 70%-exceptional photoluminescence intensity for III-V semiconductor nanocrystals. In larger InAs cores there is a systematic decrease in the quantum yield, with a yield of approximately 40% for intermediate size cores down to a few percent in large cores. The CSS structures also exhibit very good photostability, vastly improved over those of organically coated cores, and transformation into water environment via ligand exchange is performed without significant decrease of the quantum yield. These new InAs/CdSe/ZnSe CSS nanocrystals are therefore promising near-IR chromophores for biological fluorescence tagging and optoelectronic devices.     

One-pot noninjection synthesis of Cu-doped Zn(x)Cd(1-x)S nanocrystals with emission color tunable over entire visible spectrum

Unlike Mn doped quantum dots (d-dots), the emission color of Cu dopant in Cu d-dots is dependent on the nature, size, and composition of host nanocrystals (NCs). The tunable Cu dopant emission has been achieved via tuning the particle size of host NCs in previous reports. In this paper, for the first time we doped Cu impurity in Zn(x)Cd(1-x)S alloyed NCs and tuned the dopant emission in the whole visible spectrum via variation of the stoichiometric ratio of Zn/Cd precursors in the host Zn(x)Cd(1-x)S alloyed NCs. A facile noninjection and low cost approach for the synthesis of Cu:Zn(x)Cd(1-x)S d-dots was reported. The optical properties and structure of the obtained Cu:Zn(x)Cd(1-x)S d-dots have been characterized by UV-vis spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The influences of various experimental variables, including Zn/Cd ratio, reaction temperature, and Cu dopant concentration, on the optical properties of Cu dopant emission have been systematically investigated. The as-prepared Cu:Zn(x)Cd(1-x)S d-dots did show PL emission but with quite low quantum yield (QY) (typically below 6%). With the deposition of ZnS shell around the Cu:Zn(x)Cd(1-x)S core NCs, the PL QY increased substantially with a maximum value of 65%. More importantly, the high PL QY can be preserved when the initial oil-soluble d-dots were transferred into aqueous media via ligand replacement by mercaptoundeconic acid. In addition, these d-dots have thermal stability up to 250 °C.     

Synthesis of Cysteine-Capped Zn(x)Cd(1)(-)(x)Se alloyed quantum dots emitting in the blue-green spectral range

Alloyed ZnxCd1-xSe quantum dots (QDs) have been successfully prepared at low temperatures by reacting a mixture of Cd(ClO4)2 and Zn(ClO4)2 with NaHSe using cysteine as a surface-stabilizing agent. The photoluminescence (PL) spectra of the alloyed QDs are determined on the basis of the Zn2+/Cd2+ molar ratio, reaction pH, intrinsic Zn2+and Cd2+ reactivities toward NaHSe, concentration of NaHSe, and the kind of thiols. A systematic blue shift in emission wavelength of the alloyed QDs was found with the increase in the Zn mole fraction. This result provides clear evidence of the formation of ZnxCd1-xSe QDs by the simultaneous reaction of Zn2+ and Cd2+ with NaHSe, rather than the formation of separate CdSe and ZnSe nanocrystals or core-shell structure CdSe/ZnSe nanocrystals. The size and inner structure of these QDs are also corroborated by using high-resolution transmission electron microscopy and X-ray powder diffraction. To further understand the formation mechanism, the growth kinetics of Zn0.99Cd0.01Se was studied by measuring the PL spectra at different growth intervals. The results demonstrated that, in the initial stage of growth, Zn0.99Cd0.01Se has a structure with a Cd-rich core and a Zn-rich shell. The post-preparative irradiation of these QDs improved their PL properties, resulting in stronger emission.     

Synthesis and Characterization of InAs/InP and InAs/CdSe Core/Shell Nanocrystals

The effect of the outer surface of core/shell nanocrystals on the fluorescence quantum yield was observed for InAs/InP and InAs/CdSe core/shells (see picture). For InAs/CdSe we observed substantial enhancement of the fluorescence quantum yield compared to the InAs core, and up to two times larger than the laser dye IR-140. Such core/shell nanocrystals have potential use as biological fluorescent markers in the near IR spectral range.     

Synthesis of Cd-free water-soluble ZnSe(1-x)Te(x) nanocrystals with high luminescence in the blue region

Cd-free core-shell nanocrystals (ZnSe(1-x)Te(x)/ZnS, 0相似文献   

Aqueous synthesis of type-II core/shell CdTe/CdSe quantum dots for near-infrared fluorescent sensing of copper(II)

Type-II core/shell CdTe/CdSe quantum dots (QDs) were synthesized in aqueous medium by employing thiol-capped CdTe QDs as core template and CdCl(2) and Na(2)SeSO(3) as shell precursors, respectively. Compared with the original CdTe cores, the core/shell CdTe/CdSe QDs showed an obvious red-shifted emission with the color-tune capability to the near-infrared (NIR) wavelength, because of the formation of an indirect excitation. The prepared QDs exhibited high stability and moderate fluorescence quantum yields (10-20%), and their core/shell heterostructure was characterized by UV-vis absorption, steady-state and time-resolved fluorescence spectra, X-ray powder diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The fluorescence of the core/shell QDs could be markedly quenched by Cu(II), and approximate concentrations of other physiologically important cations, such as Zn(II), Ca(II), Na(I) and K(I) etc., had no effect on the fluorescence. Based on this, a simple and rapid method for Cu(II) determination was proposed using the NIR CdTe/CdSe QDs as fluorescent probes. Under optimal conditions, the response was linearly proportional to the concentration of Cu(II) between 0.05 to 50.0 x 10(-6) mol L(-1), the limit of detection was 2.0 x 10(-8) mol L(-1). The developed method was successfully applied to the detection of trace Cu(II) in real samples.     

Solvothermal synthesis of InP quantum dots and their enhanced luminescent efficiency by post-synthetic treatments

InP quantum dots (QDs) were solvothermally synthesized by using a greener phosphorus source of P(N(CH(3))(2))(3) instead of highly toxic P(TMS)(3) widely used, and subsequently subjected to a size-sorting processing. While as-grown QDs showed an undetectably low emission intensity, post-synthetic treatments such as photo-etching, photo-radiation, and photo-assisted ZnS shell coating gave rise to a substantial increase in emission efficiency due to the effective removal and passivation of surface states. The emission efficiency of the photo-etched QDs was further enhanced by a consecutive UV photo-radiation, attributable to the photo-oxidation at QD surface. Furthermore, a relatively thick ZnS shell on the surface of InP QDs that were surface-modified with hydrophilic ligands beforehand was photochemically generated in an aqueous solution at room temperature. The resulting InP/ZnS core/shell QDs, emitting from blue to red wavelengths, were more efficient than the above photo-treated InP QDs, and their luminescent properties (emission bandwidth and quantum yield) were comparable to those of InP QDs synthesized with P(TMS)(3). Structural, size, and compositional analyses on InP/ZnS QDs were also conducted to elucidate their core/shell structure.     

Size series of small indium arsenide-zinc selenide core-shell nanocrystals and their application to in vivo imaging

We have developed a size series of unusually small, water-soluble (InAs)ZnSe (core)shell quantum dots (QDs) that emit in the near-infrared and exhibit new behavior in vivo, including multiple sequential lymph node mapping and extravasation from the vasculature. The biological utility of these fluorescent probes resulted from our intentional choice to match the semiconductor material and water-soluble ligand with a desired final hydrodynamic diameter and emission wavelength.     

Highly luminescent CdSe/Cd(x)Zn(1-x)S quantum dots coated with thickness-controlled SiO2 shell through silanization

A silanization technique of hydrophobic quantum dots (QDs) was applied to SiO(2)-coated CdSe/Cd(x)Zn(1-x)S QDs to precisely control the SiO(2) shell thickness and retain the original high photoluminescence (PL) properties of the QDs. Hydrophobic CdSe/Cd(x)Zn(1-x)S core-shell QDs with PL peak wavelengths of 600 and 652 nm were prepared by a facile organic route by using oleic acid (OA) as a capping agent. The QDs were silanized by using partially hydrolyzed tetraethyl orthosilicate by replacing surface OA. These silanized QDs were subsequently encapsulated in a SiO(2) shell by a reverse micelles synthesis. The silanization plays an important role for the QDs to be coated with a homogeneous SiO(2) shell and retain a high PL efficiency in water. Transmission electron microscopy observation shows that the shells are 1-9 nm with final particle sizes of 10-25 nm, depending on the initial QD size. In the case of short reaction time (6 h), the QDs were coated with a very thin SiO(2) layer because no visible SiO(2) shell was observed but transferred into the water phase. The silica coating does not change the PL peak wavelength of the QDs. The full width at half-maximum of PL was decreased 4 nm after coating for QDs emitting at both 600 and 652 nm. The PL efficiency of the SiO(2)-coated is up to 40%, mainly determined by the initial PL efficiency of the underlying CdSe/Cd(x)Zn(1-x)S QDs.     

Versatile Tri(pyrazolyl)phosphanes as Phosphorus Precursors for the Synthesis of Highly Emitting InP/ZnS Quantum Dots

Tri(pyrazolyl)phosphanes ( 5 ^R1,R2) are utilized as an alternative, cheap and low‐toxic phosphorus source for the convenient synthesis of InP/ZnS quantum dots (QDs). From these precursors, remarkably long‐term stable stock solutions (>6 months) of P(OLA)₃ (OLAH=oleylamine) are generated from which the respective pyrazoles are conveniently recovered. P(OLA)₃ acts simultaneously as phosphorus source and reducing agent in the synthesis of highly emitting InP/ZnS core/shell QDs. These QDs are characterized by a spectral range between 530–620 nm and photoluminescence quantum yields (PL QYs) between 51–62 %. A proof‐of‐concept white light‐emitting diode (LED) applying the InP/ZnS QDs as a color‐conversion layer was built to demonstrate their applicability and processibility.     

Alloyed Zn(x)Cd(1-x)S nanocrystals with highly narrow luminescence spectral width

High-quality alloyed Zn(x)Cd(1-x)S nanocrystals have been synthesized at high temperature by the reaction of a mixture of CdO- and ZnO-oleic acid complexes with sulfur in the noncoordinating solvent octadecene system. A series of monodisperse wurtzite Zn(x)Cd(1-x)S (x = 0.10, 0.25, 0.36, 0.53) nanocrystals were obtained with corresponding particle radii of 4.0, 3.2, 2.9, and 2.4 nm, respectively. With the increase of the Zn content, their photoluminescence (PL) spectra blue-shift systematically across the visible spectrum from 474 to 391 nm, indicating the formation of the alloyed nanocrystals. The alloy structure is also supported by the characteristic X-ray diffraction (XRD) patterns of these nanoalloys with different Zn mole fractions, in which their diffraction peaks systematically shift to larger angles as the Zn content increases. The lattice parameter c measured from XRD patterns decreases linearly with the increase of Zn content. This trend is consistent with Vegard's law, which further confirms the formation of homogeneous nanoalloys. These monodisperse wurtzite Zn(x)Cd(1-x)S nanoalloys possess superior optical properties with PL quantum yields of 25-50%, especially the extremely narrow room-temperature emission spectral width (full width at half-maximum, fwhm) of 14-18 nm. The obtained narrow spectral width stems from the uniform size and shape distribution, the high composition homogeneity, and the relatively large particle radius, which is close to or somewhat larger than the exciton Bohr radius. The process by which the initial structure with random spatial composition fluctuations turns into an alloy (solid solution) with homogeneous composition is clearly demonstrated by the temporal evolution of the PL spectra during the annealing progress.     

Quantum-dot growth simulation on periodic stress of substrate

InAs quantum dots (QDs) are grown on the cleaved edge of an In(x)Ga(1-x)AsGaAs supperlattice experimentally and a good linear alignment of these QDs on the surface of an In(x)Ga(1-x)As layer has been realized. The modulation effects of periodic strain on the substrate are investigated theoretically using a kinetic Monte Carlo method. Our results show that a good alignment of QDs can be achieved when the strain energy reaches 2% of the atomic binding energy. The simulation results are in excellent qualitative agreement with our experiments.     

O2结构Liy[Mn1—xMx]O2（M＝Cr，Mg）的合成及结构研究

由高温焙烧法制备层状前驱体Na_(2/3)[Mn_(1-x)M_x]O_2（M＝Cr, Mg），再 经离子交换反应得到层状O2结构产物Li_y-[Mn_(1-x)M_x]。XRD表明Li_y[Mn_(1-x) M_x]O_2属六方晶系，P3ml空间群。Cr的添加量对前驱体的晶体结构有很大影响： 随着x值的增大，前驱体逐渐由层状P2结构Na_(2/3)[Mn_(1-x)Cr_x]O_2向正交结构 Na_4Mn_90_(18)转变。由SEM可以看到样品Li_y[Mn_(1-x)Cr_x]-O_2(x≤0.05)具有 六方层状结构。XPS分析结果表明样品Li_y[Mn_(0.95)Cr_(0.05)]O_2表面上的Mn和 Cr分别以Mn~(4+)存在，并且表面中Cr相对含量高于体相，而样品Li_y[Mn_(0.90) Mg_(0.10)]O_2的表面Mn和Mg分别以Mn~(4+)和Mg~(2+)存在，Mg/Mn比在表面与体相 基要一致。     

InAs(x)Sb(1-x) alloy nanocrystals for use in the near infrared

InAs(x)Sb(1-x) alloy nanocrystals for the near-infrared, which have quite a monodisperse crystalline structure of 2.5-3.0 nm and are of a zinc blend structure, are developed.     

Low power operated highly luminescent ferroelectric liquid crystal doped with CdSe/ZnSe core/shell quantum dots

We report the enhancement in the molecular ordering of ferroelectric liquid crystal (FLC) doped with CdSe/ZnSe graded core/shell (CZ) quantum dots (QDs) by using optical methods. Significant decrease in operating voltage and enhancement in optical brightness are assigned to the large primary order parameter (θ) and hence anchoring of FLC molecules by CZ QDs. The enhancement in photoluminescence is conjectured to be due to an increase in molecular alignment yielding higher absorption which is confirmed by excitation spectra. These observations would definitely offer a promising tool to get superior core/shell QD incorporated FLC-based display devices.